1. Field of the Invention
The present invention relates to a pneumatic tire which is provided with a shoulder land portion extending in a tire circumferential direction on a tread surface, and a narrow groove extending in the tire circumferential direction on the shoulder land portion.
2. Description of the Related Art
In a rotating pneumatic tire, a ground pressure generally tends to be higher in the vicinity of a around end of a shoulder land portion of a tread surface. As a result, there may arise a problem of irregular wear in which an amount of wear in the vicinity of the ground end of the shoulder land portion becomes larger in comparison with the other land portion of the tread surface. As a method of preventing the irregular wear mentioned above, there has been widely carried out a reduction of a rigidity of the shoulder land portion by forming a narrow groove extending in the tire circumferential direction in an inner side in a width direction than the ground end, in the vicinity of the ground end of the shoulder land portion of the tread surface.
Further, in a heavy duty pneumatic tire, particularly in a rib tire, there has been known the matter that a ground pressure is lowered by setting a narrow groove or a depression extending in a tire circumferential direction in a groove wall constructing a rib end portion for the purpose of preventing irregular wear of a rib end portion so as to suppress a rigidity of the rib end portion (refer, for example, to Japanese Unexamined Patent Publication No. H09-2018).
However, if the groove wall is provided with the narrow groove extending in the tire circumferential direction, a step caused by the narrow groove is generated on the tread surface in the process of wear and this is not preferable.
Further, in the Japanese Unexamined Patent Publication No. H09-2018, there is disclosed a pneumatic radial tire in which a plurality of concave portions having a depth in a transverse direction are formed in a groove depth direction, on a groove wall close to an inner side in the transverse direction of a main groove or an auxiliary groove, for the purpose of suppressing a rigidity of a land portion. However, a ground pressure becomes lower at a position where the concave portion exists in the groove wall, the ground pressure becomes higher at a position where the concave portion does not exist, and a ground pressure of a rib end portion becomes uneven in a circumferential direction, so that an irregular wear resistance is not sufficient.